High frequency ceramic microcircuit packages were introduced in the 1980's, examples of which are shown in U.S. Pat. Nos. 4,942,076 and 5,089,881. Such packages allow fine pitch microcircuit packaging with multi-layer and metal filled vias. The multi-layer ceramic substrate with metal filled vias provided the “water tight” hermeticity of the base of the microcircuit. Hermeticity of the device mounted inside this package was achieved by soldering onto the package a metal wall around the device and then soldering a metal lid to the metal wall. Alternatively, a combination metal lid and sidewall could be soldered into place. Hermeticity in this context is defined as achieving a leak rate less than 1×10E-8 CC/Second of Helium. The soldered (or brazed) metal sidewall and lid solution is expensive to manufacture due to the fine metal detail needed to manufacture the covering package lid. Precision soldering the covering package lid to the circuit also adds to the cost.
One solution to the cost issue that has been used where mechanical protection is required for the device but hermeticity is not required is to epoxy a low cost ceramic package lid over the device using a dry nitrogen atmosphere. Ceramic packages have been found to allow Gallium Arsenide (GaAs) ICs circuits to fail because water vapor penetrates the package lid (housing) around the circuit. This water vapor has been thought to pass through the epoxy seal but not through the walls of the housing itself.